There is a continuing need in the art of manufacturing plastic parts to reduce the manufacturing costs while maintaining product quality. Many different types of plastic fillers have been proposed for use with molded plastics, but all have failed for one or more reasons. This is particularly true for rotational molded parts.
For instance, organic materials, such as crushed nut shells, produce harmful gasses at typical molding temperatures of 550.degree. F. to 700.degree. F. Sand has also been tried as a filler, but it does not mold well because it does not disperse evenly through out the plastic. Instead, sand tends to migrate to the inside of rotational molded parts. It does not bond well with the plastic and sheds quickly. Sand is also hard on the mixing equipment. Commercially available glass beads and whiskers are often used with injection molded plastics. They have been used with varying degrees of success in rotational molded plastics because the glass does not mix well and simply balls up on the inside of the rotating mold. As used herein, a plastic "filler" is an ingredient which has a cost substantially less than the cost of the plastic used to mold the product. As used herein, a plastic "reinforcement" is an ingredient which is included in the plastic to provide a desired property or characteristic to the molded product.
As mentioned above, specially manufactured glass has been used as an ingredient in injection and rotational molded plastic parts. For instance, commercially available glass fibers or whiskers, having a length of about 1/4 inch, have been added to plastic to make the product tougher and to improve the yield stress. Manufactured glass beads (either solid or hollow) have also been used in injection and rotational molded plastics to improve to toughness and abrasion resistance of the product. However, the manufactured glass fibers and beads cost approximately the same as the plastic used to mold the product. The manufactured glass fibers and beads have been used solely to provide desired mechanical properties in the finished plastic product. They have not been used as a filler in plastic to reduce manufacturing costs.
It would be a significant advancement in the art to provide a true filler for molded plastic parts which can be used to lower the manufacturing cost of molded plastics. It would also be an advancement in the art to provide a filler for molded plastic parts which enhances certain mechanical properties of the part and functions as a reinforcement ingredient.
Such a filler for molded plastic parts is disclosed herein.